The _______ of weak entity set distinguishes among all those entities in the weak entity set that depends upon one particular strong entity.

Question

Accepted Answer

The correct option is (2):
The correct term is the **Discriminator**, which is also known as a partial key. By definition, a weak entity set cannot be uniquely identified by its own attributes alone, as its existence is dependent on an instance of a strong entity set (its owner). Therefore, the discriminator is the set of attributes that can uniquely identify the entities *within* a single, particular instance of the strong entity. For example, in an "Employee" (strong) and "Dependent" (weak) relationship, the Dependent entity's discriminator might be the dependent's name, which is unique only for one specific employee, but not globally across all dependents. The full primary key of the weak entity is formed by combining the strong entity's primary key and the weak entity's discriminator.

The incorrect option is (1) Primary key:
A Primary Key is an attribute or a set of attributes that uniquely identifies every entity within an entire entity set across the entire database. However, a weak entity set does not possess a primary key of its own; this is the fundamental reason it is classified as "weak." The full Primary Key for a weak entity set is actually constructed from the primary key of its associated strong entity *plus* the weak entity's discriminator. Simply calling it the Primary Key would be inaccurate as it lacks the necessary global uniqueness without the strong entity's identifier.

The incorrect option is (3) Identifying Relationship:
The Identifying Relationship is the structural *type* of relationship, often represented by a double diamond in an E-R diagram, that links the strong entity set (the owner) to the weak entity set. It describes the dependency and how the two entity sets are connected, signifying that the weak entity's identity is derived through this connection. However, it is a *relationship*, not the actual attribute or set of attributes used for unique identification.

The incorrect option is (4) Candidate key:
A Candidate Key is a general term in relational database theory for any minimal set of attributes that could potentially serve as a Primary Key for a relation. While the combination of the strong entity's primary key and the weak entity's discriminator *forms* the primary key (which is a candidate key), the specific term for the distinguishing part *within the weak entity itself* is the **Discriminator**. This term is crucial in E-R modeling to highlight the partial nature of the key.